The present invention relates to a reversible adsorbent for carbon dioxide which can be used as a decontaminant of closed environments and a method for producing the adsorbent.
It has been known for some time that modified silica gels could be used as adsorbents and catalysts. In his article "Modified Silica Gels As Adsorbents and Catalysts," Chemical Technology, Vol. 4, No. 6, June 1974, pp 370-377, Professor Robert L. Burwell, Jr. discusses the use of modified silica gels as adsorbents. Professor Burwell reports that studies have been conducted on the adsorption of CO.sub.2, H.sub.2 S and SO.sub.2 by modified silica gels. The test work involved passing a helium carrier gas through a bed of modified silica gel that is first activated at about 175.degree. C. to remove adsorbed water; injecting a sample of CO.sub.2, H.sub.2 S or SO.sub.2 ; and releasing the adsorbed material by temperature programmed desorption at a rate of about 30.degree. per minute. Professor Burwell also reports that aminomodified gels have been used to trap carbon dioxide during tests to measure the amount of carbon dioxide in a particular environment.
In the article "Modified Silica Gels as Selective Adsorbents for Sulphur Dioxide," Journal of the Chemical Society Chemical Communications, 1974, pp 342-3, Professor Burwell and Mr. Orlando Leal briefly note that silica gel, chemically modified by conversion into--CH.sub.2 --CH.sub.2 CH.sub.2 NH.sub.2, where o represents a silicon atom at the surface of the silica gel, selectively adsorbs carbon dioxide. The adsorbed gas is liberated by temperature programmed desorption at about 100.degree. C. The article continues on to discuss a modified silica gel which adsorbs sulphur dioxide.
In the article "Reversible Adsorption of Oxygen on Silica Gel Modified by Imidazole--Attached Iron Tetraphenylporphyrin" by Orlando Leal et al., Journal of the American Chemical Society, Vol 97, pp 5125-5129, the authors describe the adsorption of oxygen on an iron (II) porphyrin attached to the imidazole groups of a silica gel containing 3-imidazolylpropyl groups bonded to surface atoms of silicon.
None of these articles however teach or suggest how to produce a commercially viable absorbent capable of diminishing the ambient concentration of carbon dioxide in open or closed environments.
Accordingly, it is an object of the present invention to provide a novel reversible adsorbent which can be used to diminish the ambient concentration in open or closed environments.
It is a further object of the present invention to provide an adsorbent as above which can be used to concentrate o scrub carbon dioxide out of gas streams where it is present as a contaminant.
It is yet a further object of the present invention to provide an adsorbent which is regenerable under rather moderate heating conditions.
It is still a further object of the present invention to provide a process for forming the above adsorbent.
These and other objects and advantages will become more apparent from the following description and drawings in which like reference numerals depict like elements.